The sun is too low in winter and the atmosphere blocks the UVB rays our skin needs to produce Vitamin D. The same thing happens around sunrise and sunset even

The sun is too low in winter and the atmosphere blocks the UVB rays our skin needs to produce Vitamin D. The same thing happens around sunrise and sunset even in summer. Here's a good explanation from HN's favorite site: https://physics.stackexchange.com/questions/268509/why-is-there-less-uv-light-on-earth-in-winter https://physics.stackexchange.com/questions/268509/why-is-th...